Fluid level indicator



y 8, 1952 D. SEBASTIAN ET AL 2,602,848

FLUID LEVEL INDICATOR Filed Dec. 14, 1950 INVENTORS DAVID SEBASTIAN BERNT J. HEGGEN ROB E RT H. HAMPTON BY THEIR ATTORNEY Patented July 8, 1952 FLUID LEVEL INDICATOR David Sebastian, Bernt J. Heggen, and Robert H. Hampton, Brooklyn, N. Y., assignors of fifteen percent to Joseph L.'Klein, New York,

Application December 14, 1950, Serial No. 200,812

'7 Claims. (Cl. 177311) This invention relates to fluid level indicators, and more particularly to a device for determining the level of liquids.

The specific embodiment of the indicator to be disclosed hereinafter, and shown by way of illustration only, is designed for measuring the level of hydraulic fluid in the supply tank of the hydraulic'brake system commonly used in automobiles, trucks and similar vehicles. The purpose of the indicator is to signal the driver of the vehicle whenever the level of the hydraulic fluid falls to or below the danger level--that is, the level below which there is the danger of failure of the brakes due to an inadequate supply of brake fluid.

Several forms of liquid level indicators have been designed to accomplish this purpose, however these devices, for the most part, have inherent disadvantages which preclude their general acceptance. For example, in the well known float-type level indicator, the float becomes gummed by the hydraulic fluid so that the float sticks and thereby renders the indicator inoperative. Several electrically operated indicators have been designed to overcome this disadvantage of the float-type indicator. Of these, some are too expensive and delicate; others depend on the electric conductivity of the fluid for their operation, but the conductivity of the various hydraulic fluids available vary to such a degree as to make such an indicator impractical.

' The present invention'inv'olves an electrically operated indicator with a single moving part sealed oii from the hydraulic or other fluid thereby obviating any possibility of the device becom ing inoperable due to the action of the fluid on the indicator. The operation of the device is independent of the electrical conductivity of the fluid. Moreover, the present invention utilizes the fewest possible parts in its design thereby not only minimizing the cost of the device, but also simplifying it to such an extent that the possibility of the indicator becoming inoperable is minimized.

It is one object of this invention to provide a liquid level indicator which is relatively simple prevent overheating of the heater utilized in. the

indicator.

Other objects of the invention will become apparent from the following specification and drawings in which Figure 1 is a sectional elevation of a preferred form of the liquid level indicator and the associated electrical signal circuit,

Fig. 2 is a transverse view taken through Figure 1 along the lines 2-2 looking in the direction of the arrows and shows the movable con tact elements of the indicator,

Fig. 3 is a transverse view through Figure 1 taken along, the line 3--3 looking in the direction of the arrows,

Fig. 4 isv a transverse view taken through Figure 1 along the line 4-4 looking in the direction of the arrows and shows the heating unit of the indicator,

Figures 5, 6 and '7 are side views of the movable contact elements shown in different operative positions; and

Fig. 8 is a transverse view taken through Figure 1 along the line 88 looking in the direction of the arrows and showing the electrical contact rings on the indicator.

Referring to the drawings, Figure 1 shows a preferred form of the indicator mounted within a tank [0 partially filled with hydraulic fluid or other liquid. The indicator comprises, in general, a fluid tight container 1 i to which is adapted a heater l2 projecting into the hydraulic fluid. Mounted within the container H are a pair of thermo-sensitive bi-metallic bars ['3 and i M which are actuated responsively to variations in temperature of the heater [2 to make and break 'a heater circuit [5 and a signal circuit I6.

During normal operating conditions, i. e., wheneverthe level of the liquid within the tank in is above some predetermined level, heat is conducted from the heater [2 by the surrounding liquid thereby preventing the temperature of the heater from exceeding some predetermined value; under these conditions the bar 14 maintains electrical connection between. the heater i2 and a supply of electrical powersuch as the battery ll. In the event the liquid level should fall below some predetermined level so that a portion of the heater [2 is exposed to the air or any other medium having a coeflicient of heat conductivity which is less'than that of the liquid in the tank If], then, due to the increase in temperature-of the exposed portion of the heater, the bar 13. will deflect to complete the signal circuit [6 thereby giving warning that the level of the liquid within the tank [0 has fallen below the aforesaid predetermined level.

Asfa safety feature, the bi-metallic bar 14 is designed to deflectand break the heater circuit {5 wheneverthe temperature of the, heater l2 exceeds some predetermined value thereby precluding any possibility of the heater or other elements of the indicator becoming excessively hot in the event the heater is entirely exposed to the air for a long period of time. In the preferred form of the indicator, the temperature value at which the bar I4 breaks the heater circuit is somewhat higher than the temperature value at which the bar I3 completes the signal circuit. Moreover, the temperature at which the bar It closes the heater circuit is somewhat higher than the temperature value at which the bar I3 opens the signal circuit. In operation this means that whenever the signal circuit is completed, the heater circuit can be intermittently ,exteriorly of the tank It with the heater I2 extending into the tank, if desired, and in-which case the container need not be fluid tight. EX- tending through the perforation I8 in the container is the heater l2 which comprisesa hollow heat conducting member I 9 having a closed outer end to house a heating unit or coil located within that portion of the member Ifi-lying exteriorly of the chamber II.

The opposite, or inwardly, end of the member I Sis flared outwardly in the form of a Washer 21 on which are mounted the bi-metallic bars I3 and I4. In the preferred form of the invention, the bars I3 and I4 are riveted atoneend to the member. I9, or otherwise held in firm heat conductive contact therewith; and in furtherance to the .end that the member IBserve as-a means .for convvducting the heat from the coil 28 to the bars I3 and I4, the thickness of the wall of the member I 9 is relatively greater than the thickness of the Wall of the container II so that a greater portion of the heat conducted along the wall of the member I9 is conducted to the washer 2I and the bi-meta'llic bars I3 and i4 rather than along the wallof the container II.

Mounted in face relation with the washer 2I is a fiber, or plastic, plate 28 on which aremounted contact buttons. 21 and29 connected, respectively, inthe power circuit I5and signal circuit I6. The plate 28 is mounted in such wise relative .to.the washer 2i so that .whenever the free ends oflthe bars I3 and I4deflect to their-upper limitingposition, the signal and heater circuits, respectively, are completed. That is, the button 29 is contacted by a button 30 on the free endof thelbar I3 whenever the bar I3 deflects into its uppertoward the plate 28-limiting position,

and the insulated freeend of the bar I4 when deflected in the upwardly direction, as viewedin Figure 1, will contactand force in thatdirection the free end of a resilientelectrically conducted strip, or bar, 24 mounted on the plate 28. The bar I 4 in its upper limiting position holds a contact butt-1011.26 on bar 24 in contact with; the button 2.7. The bar 24 is connected by a wire 43, which extends through a-plastic plug-23 sealing the open end of the bore 22, to the-coil 29 so that whenever the bi-metallic bar. I4 assumes said limiting position, electrical connection is-made between the heater I2 and the power circuit I5.

Suchalignmentof the contact button 2! with the button 26 and the button 30 with the button 29 is assured by the expedient of mounting the plate 28 on shoulder pins 42, press fitted in the washer 2!. These pins 42 also maintain the proper distance between the plate 28 and the washer =2I so that contact is made and broken between such contact points, or buttons, at the required liquid levels aforesaid.

In the embodiment of the invention illustrated, the container II and associated heater and contact assembly is mounted within the tank I0 on a tube 3i, press fltted in a plug 33, threaded in the tank IE3. The lower or inner end of such tube 3| extends through a cover 32 for the container I I and is provided with a shoulder M at its lower end upon which the inner surface of the cover '32 rests. It is to be noted in this connection that is readily adaptable to any existing hydraulic system provided with such tank, and it is merely necessary to drill a hole in the plug 33 and press fit the tube 3i therein.

--Encirc1ing the outer end, the upper end as viewed in Figure 1, ofthe tube .3I are a pair of metallic rings'34 and 35. These rings are insulated from the member 3i by means of insulation 36 thereby permitting one of the rings, in the drawing, ring, to be connected to the button 29 bymeans of a lead 31 extending along the interior of the member 3 i; and the other ring, ring 35, to be connected to the button 2'! by ahead 38, hence any conventional electrical cap (not shown) may be slid over the contact rings Stand 35. For the purpose of simplicity however, leads 39 and 4B .in the signal and heater circuits, respectively, are connected directly to the rings34 and ,35.

Tracing the electrical circuits in detail, the heater circuit vstarting with ground connection 43 on the negative side of the battery I7, theposiwtiveside-of the battery is connected through lead .to the ring 35 which in turn is connected by lead-38 to the button 21'. Under normal operatingconditions, the metallic bars I3 and I4 assume the position shown in: Figure 6 and hence the conductive strip 24 is held in contact with the button 27 therebyconnecting one endof the coil 29 with the battery IT. The opposite end of the coil ZO-is connected to the lower end of the member I9 and the member I9 is grounded through the container II, tube 3|, plug ;33 and tank ID to the ground 44.

In order to prevent grounding the wire of the coil-2e against the side of the member I9, the porcelain plug on which the coil is wound, is provided with grooves 46 of greater depth than the diameter of the wire in the coil 253. It is also to be noted in this connection, that although the coil:20 does not contact the member I9, other than at its point of connection at the bottom as previously mentioned, it is positioned immediately adjacent thereto so that the heat of the coil is readily conducted throughthe walls of-the member I9 to the surrounding liquid Tracing the signal circuit I6,uagain starting from the ground 43. connectedto thenegative side of the battery II, the positive side of the battery is connected by lead 39 to the contact button 29, a signallight 41 being connected in this lead 39. This circuit is completed through the bar I3-when the buttons 29 and 30 are in contactethe member I9, container II, member 3I, plug 33 and tank I to ground 44.

Reviewing the operation of the indicator, it will be assumed that the level of the liquid in the tank I0 is as shown in Figure l, or in other words, that-the heater I2 is substantially immersed in liquid. Undersuch a condition, the bi-niet'allic bars I3' and I4 will take the position shown in Figured-i. e., the bar I I is deflected in the upward position to'for'ce thebutton 26 on the strip 24' into contact with the button 21 to make, or complete, the heater circuit, and the bar I3 is deflected to break, or disconnect, the signal circuit I6. In other words, the heater circuit I5 is completed sothat the heater 12 generates a quantity 'of heat which, for the most part,'is dissipated in heating the liquid in the tank I0.

In the event that the level of the liquid'in the tank'lfl falls below some predetermined leveliso as to expose at least a portion of the heat conducting member I9 to the air in tank I0, then a portion of the heat normally dissipated by the liquid is conducted by the wall of the member I9 to the washer 2I;:and hence to the bi-metallic bars I3 and I4. At some predetermined temperature of the washer 2I, the bi-metallic bar I3 will deflect, in the upwardly direction as viewed in Figure 1, to establish contact between the buttons 29 and 30 and thereby complete the signal circuit I6 and causing the light 41 to glow to indicate that the liquid level in the tank ID has fallen below the aforesaid predetermined level. Under these conditions, the bars I3 and I4 take the position shown in Figure 5.

If at this lower liquid level, the temperature of the heater I2 exceed-s some predetermined value, a value at which there is a danger that the coil 20 will burn out or adjacent parts will be damaged, the bar I4 will deflect downwardly to break the heater circuit I5 (see Figure 7). Under these conditions, the heater l2 will be permitted to cool thereby precluding the burning out of the coil, but the bars I3 and I4 are so chosen that before they heater. cools down to a temperature value at which the bar I3 will deflect to break the signal circuit I 6, the bar I4 will again return. to the position shown in Figure 5 to complete the'heater circuit. In other words, the heater circuit I5 is periodically interrupted to prevent overheating of the heater I2, but these interruption-s are of such short duration that the temperature of the washer 21 does not fall to a value which will permit the bar l3 to break the signal circuit.

It is also important to note in connection with the present invention, that the level indicating device is located with its center line coinciding with the center line of the tank I 0 so that any inclination of the tank III with respect to the horizontal will not disturb the operation for the indicating device. For example, if the signal device were located at an end of the tank I0, inclination of the tank in a direction toward the indicator would permit the level of the liquid to fall below the danger point without the signal device operating the warning light 41, and inclination of the tank in the opposite direction would result in the indicator signaling a dangerous liquid level although an adequate quantity of liquid were present in the tank.

In view of the foregoing disclosure it is readily apparent that the present invention accomplishes, among others, the objects hereinbefore stated, and provides a liquid level indicator which is relatively simple in construction and comparatively inexpensive both in initial cost and upkeep.

6 Moreover,- due to'its simplicityof construction and design, the possibility of the device becoming inoperable is minimized-an extremelyimportant feature when it is realized that an indicating'device such as this is ofen used as a warning indicator in which case one of the required features is that the operation of the device must be reliable. It is also important to note that-the indicator herein disclosed may be readily adapted to existing fluid systems with little or no change in the system.

While we have shown and described a specific form of our'inventio-n, it is to be understood that various changes and modifications may be-made without departing from the spirit of the invention as set forth in the appended claims.

We claim: I

l. A fluid level indicator for use in an electrical signal circuit, comprising a container, a heater extending into the fluid the level of which is to be measured, means for conducting heat from the heater into the container, and a thermo-responsive element mounted in thermal contact with said means within saidcontainer and connected in the signal circuit, said elements being adapted to act in response to variations in temperature of said means for completing the signal circuit whenever the level. of said liquid falls below some predetermined level and breaking said circuit whenever such level exceeds a predetermined level. i r

2. A fluid level indicator comprising a fluid tight container, a member in said container and having a pair of electrical contacts thereon for connection with a signal circuit and a source of power, a heat conducting member having an end located within said container and a, portion pro jecting from thecontainer into the fluid the level of which is to bemeasured, a heating unit positioned within said portion for heating said heat conducting member and sealed from contact with such fluid, a thermo-sensitive element mounted on said end of' the heat conducting member and designed, to maintain electrical contact between the heating unitand-one ofsaid electrical contacts whenever thetemperatureof the heat conducting member is below some predetermined value and to deflect and break such connection whenever the temperature of the heat conducting member exceeds said value, and another thermo-sensitive element mounted on said end of the heat conducting member and designed to deflect and contact the other of said contacts whenever the level of said liquid ,falls below some predetermined level and to deflect and break such contact whenever the level of such liquid rises above such point.

3. A fluid level indicator comprising a container, a heat conducting member adapted to said container and having a portion located within the container and a portion positioned exteriorly of the container in the fluid the level of which is to be measured, a member within the container and adjacent the first said portion of the heat conducting member and having an electrical contact point thereon for connection with a signal circuit, a heating unit positioned within the last said portion of the heat conducting memher and sealed from contact with said fluid, and a thermo-sensitive member mounted on the first said portion Of said heat conducting member and designed to deflect and contact said point Whenever the level of said liquid falls below some pre determined level.

4. A liquid level indicator comprising, a source of-electrical power, a signalcircuit, a heater extending into the liquid the level of which is to be measured, a thermo-sensitive element acting responsively to variations in temperature of said heater to. deflectand connect the heater to said source of power whenever the temperature of the heater is below some predetermined value and to deflect and disconnect the heater from said power source wheneverthe temperature of the heater is above said value, and a second thermosensitive element responsive to variations in temperature of said heater to make and break the signal circuit in accordance with the level of such liquid.

' 5. A liquid level indicator comprising, a source of electrical power, a signal circuit, a liquid tight container, a heat conducting member-having a portion located within said container and a portion extending into the liquid the level of which is to be measured, a heating coil positioned within the last said portion of the member and connected to said power source, an electrical contact point positioned withinsaid container and connected in said signal circuit, and a thermo-sensitive element adapted to the first said portion of the heat conducting member and responsive to variations in temperature thereof to deflect and contact said point to complete the signal circuit whenever the level of such liquid falls below a predetermined level.

6. A fluid level indicator for a tank containing a liquid, comprising a fluid tight container within the tank, a heat conducting member mounted on said container and having a flatted end portion located within the container and the other end portion of said member projecting into the liquid the level of which is to be measured, a heating coil in the last said portion of the member and sealed therein from contact with such liquid, a plate positioned within said container and having a contact thereon for connection witha signal circuit, supports mounted on said member and connected to hold said plate in spaced relation with said fiatted portion, a thermo-sensitive element secured in heat conducting relation to said flatted portion and arranged to deflect and engage said contact to operate the signal circuit whenever the level of the liquid falls below a predetermined level.

'7. A fluid level indicator for a tank containing a liquid, comprising a fluid tight container within the tank, a heat conducting member mounted on said container and having a flatted end por-' tionlocated within the container and the other end portion of said member projecting into the liquid the level of which is to be measured, a

heating coil in the last said portion of the memher and sealed therein from contact with such liquid, a plate positioned within said container and having thereon a contact for connection with a signal circuit and a contact for connection with a heater circuit, supports mounted on said member and'connected'to hold the plate in spaced relation with said flatted portion, a thermosensitive element for connection in the signal circuit and secured in heat conducting relation to said flatted portion, said element being adapted to deflect and engage the first said contact and to deflect and move out of engagement with such contact in response to variations in the level of the liquid to be measured, and a second thermo-sensitive element connected to said heating coil and'secured in heat conducting relation to said flatted portion and arranged to deflect and engage the second said contact to complete the power circuit whenever the temperature of said heater falls below a predetermined value and to deflect and break the power circuit whenever the temperature of the heater exceeds a predetermined value.

DAVID SEBASTIAN.

BERNT J. HE'GGEN.

ROBERT H. HAMPTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

